Magnetocaloric material is alternately moved into a magnetic field and out of the magnetic field in heat pumps that operate by utilizing the magnetocaloric effect. A spin alignment of the electrons of the magnetocaloric material takes place under the influence of the magnetic field during the moving into the magnetic field. This spin alignment or alignment of the magnetic moments in the magnetic field results in the magnetic entropy decreasing. Because the overall entropy of the system cannot decrease, a thermal entropy manifesting itself in a rise in temperature is increased. The reverse process takes place if the magnetocaloric material is moved out of the magnetic field. The temperature of a magnetocaloric material moved out of a magnetic field decreases.
Because only minor differences in temperature can be brought about by utilizing the magnetocaloric effect compared to thermodynamic processes used in conventional cooling devices or heat pumps, it is necessary to carry out multistage processes, in which a successive temperature change is obtained by means of connecting in series a plurality of systems using the magnetocaloric effect, for providing a temperature change of the magnetocaloric material exceeding these temperature differences or of a fluid absorbing heat from said magnetocaloric material.